As the DOTP2013 expansion analysis indicated, guilds are confirmed back in the first two (large) sets of Return block, followed by a third (small) set containing cards for all ten guilds.
Return to Ravnica: Azorius, Izzet, Rakdos, Golgari, Selesnya.
Gatecrash: Orzhov, Dimir, Gruul, Boros, Simic.
"Sinker": Everybody!
None of the original guild keywords are returning; each guild gets a new keyword which is supposed to play well with the old keyword. Some of the guildmasters are either the same or previously existed in the story, notably Borborygmos of the Gruul, Niv-Mizzet, Isperia of the Azor, Rakdos, the Ghost Council, and Jarad a Golgari elf who was Savra's brother and wound up opposing her in the Ravnica block novels, in which he died, manifested as a spirit, and possessed his own dead body, spontaneously animating as a lich. New guildleaders include a three-in-one dryad for the Selesnya, a merfolk for the Simic (merfolk appearing on Ravnica is apparently a story-relevant development), a new Boros angel, and some guy for the Dimir (some people are suggesting that this guy was previously a dark confidant).
Two planeswalkers in the first set, one of whom is Jace; two planeswalkers in the second set, one of whom is Gideon (who is blatantly Boros-aligned red-white at the moment).
At the prerelease, you declare your allegiance to one of the five guilds. This gets you a special "guild box" with an appropriate spindown life counter, a guild-specific promo card that you can actually use in the tournament, a guild sticker, a letter from your guildmaster, 5 packs of Return to Ravnica plus one guild-aligned pack that contains only cards of your guild's colors, and an achievement card with guild-specific achievements.
They have all-but-confirmed the existence of the shocklands.
Commander is becoming a yearly product to replace the premium deck series. However, they couldn't start this in time for this ear, so the product this year is a special reprints-only set with new art and frames.
Also a land was spoiled for the FTV:Realms that adds 1 mana of any color but puts a 1/1 colorless spirit into play under an opponent's control.